Behold, a challenger approaches the ivory tower

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Physics Guy
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Re: Behold, a challenger approaches the ivory tower

Post by Physics Guy »

Tunnelling isn't something we are free to turn on or off, because it isn't really a separate phenomenon from ordinary motion of microscopic particles. It's an inherent part of how they move, and they will do it, to whatever degree they do it, whether we want it or not. Everything tunnels, in theory at least. It's just a matter of how probable it is to get past an opposing force by tunnelling.

You can work out that probability; it's not a mysterious anything-might-happen deal, and unfortunately it's also not something that we can change artificially. To work out the tunnelling probability exactly, for, say, proton-tritium fusion, is pretty hairy, because the strong force in full detail is really a nightmare. But you can make a ballpark estimate pretty quickly with a single integral.

I might have made some arithmetic slips but what I estimate is this. If you're at room temperature, the estimated probability of fusion in a collision between two nuclei, without considering tunnelling, is somewhere around 1 in 10 to the ten-thousandth power. Even if I've missed a few factors of two or something, I really doubt it's going to be better than one in 10 to the thousand. Not even Mormon apologists consider probabilities this low.

Raising the temperature, so that your nuclei can get closer to each other just by momentum before they have to start tunnelling, helps a lot. You still have to get really high temperatures before you have any significant chance of fusion, though. Tunnelling is included in the calculations people make of what temperatures you need; it's one of the effects that brings them down from the billion-degree range that you would naively estimate to merely tens of millions.
What if fire is only the first of a million such things?
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Re: Behold, a challenger approaches the ivory tower

Post by malkie »

"Being God is hard work. You know you’ve done your job right when no one is quite sure if you’ve done anything at all." - drumdude
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